Multiple window pad assembly

ABSTRACT

A method and apparatus for detecting and obtaining a metric indicative of a polishing process is described. The apparatus includes a polishing pad having an optically transparent region adapted to obtain polishing metric from at least one substrate from at least two distinct radial positions of the polishing pad. The method includes obtaining a polishing metric from at least two substrates being polished simultaneously on a single polishing pad.

CROSS-REFERENCE TO RELATED APPLICATIONS:

This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/059,622 (Attorney Docket 013037L), filed Jun. 6, 2008, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments described herein generally relate to a chemical mechanical polishing system suitable for use in semiconductor manufacturing. More specifically, to a pad assembly suitable for use in chemical mechanical polishing system.

2. Description of the Related Art

In the fabrication of electronic devices on semiconductor substrates, the use of chemical mechanical polishing, or CMP, has gained favor due to the widespread use of damascene interconnects structures during integrated circuit manufacturing. Although many commercially available CMP systems have demonstrated robust polishing performance, the move to smaller line widths requiring more precise fabrication techniques, along with a continual need for increased throughput and lower cost of consumables, drives an ongoing effort for polishing system improvements. Moreover, most conventional polishing systems have relatively limited flexibility for changes to processing routines, thereby limiting the diversity of processes that may be run through a single tool. Thus, new processing routines may require new or dedicated tools, or costly downtime for substantial tool configurational changes.

During CMP, various methods and apparatus have been developed to signal an endpoint to the polishing process. One conventional endpoint detection apparatus uses an optical sensor adapted to obtain a metric from the substrate being polished, such as a reflection from a layer or layers on the substrate, to gauge material removal and/or prevent over polishing. The conventional CMP pads may include a single, small transparent region or window that is generally transmissive to light or an electromagnetic signal as shown in FIG. 1.

FIG. 1 shows a conventional CMP station 1, partly in cross-section, that may be a stand-alone unit or part of a larger system. The CMP station 1 generally includes a platen 20 with a polishing pad 10 mounted thereon, and a carrier head assembly 30 for holding a substrate to be polished, such as a semiconductor substrate 15, against the upper surface of the polishing pad 10. The polishing pad 10 has an upper surface serving as a polishing surface which is brought into sliding contact with the substrate 15 to be polished. A polishing liquid supply nozzle 22 is disposed above the platen 20 for supplying a polishing liquid 18 onto the polishing pad 10.

The polishing pad 10 may be a polymer material, which may be solely dielectric or, alternatively, at least partially conductive to facilitate electrochemical dissolution of material from the substrate 15 in an electrochemical mechanical polishing (ECMP) process. In another conventional application, the polishing pad 10 may contain fixed abrasives. Thus, the polishing liquid 18 may be a slurry or an electrolytic fluid depending on the polishing process used.

The platen 20 is coupled to a shaft 42 and motor 21 to rotate the platen 20 and polishing pad 10 about an axis. The carrier head assembly 30 is coupled to a shaft, which is coupled to a motor and a lifting/lowering device (not shown) that is adapted to urge the held substrate 15 against the polishing surface of the polishing pad 10. The carrier head assembly 30 may be rotatable to provide movement of the held substrate 15 relative to the polishing pad 10. The carrier head assembly 30 may also be adapted to sweep the held substrate 15 in a linear or arcuate motion across the polishing surface of polishing pad 10. The carrier head assembly 30 is typically configured to hold the substrate 15 and provide movement relative to the polishing pad 10 along a pre-determined radial position or area of the polishing pad 10 during processing.

An optical sensor 40 is provided in the platen 20 for measuring a film thickness of an insulating film (or layer) or a metallic film (or layer) formed on the surface of the substrate 15. The optical sensor 40 may be coupled in or on the platen 20 as shown, or coupled to a base 35 at a suitable radial location. The optical sensor 40 is typically fixed to the base 35 in that radial location. The optical sensor 40 may be a light-emitting element and a light-detecting element or an electromagnetic signal transmitter/receiver. The polishing pad 10 has a single transparent window 41 mounted therein and aligned with the optical sensor 40 for allowing signals from the optical sensor 40 to pass therethrough. The optical sensor 40 is electrically connected to a controller and the controller is connected to a display unit 45 for inspection by a user. Although the carrier head assembly 30 rotates and/or sweeps, the location of the window 41 and/or optical sensor are typically chosen based on the substrate 15 location in the pre-determined radial area or position of the polishing pad 10 during processing in order to facilitate access of the optical sensor 40 to the substantial geometric center of the substrate 15 during rotational and/or sweeping movement.

While the conventional CMP station 1 is suitable for performing a polishing process and endpoint detection on a single substrate 15 at a pre-determined radial area of the polishing pad 10, it may not be suitable for performing a polishing process and endpoint detection on more than one substrate and/or on a system where the pre-determined radial position of the substrate may change. In one example, one or more substrates held in respective carrier head assemblies may be caused to contact the polishing pad at the same time. In another example, a first substrate may be caused to contact the polishing pad 10 at or near a perimeter of the polishing pad 10, while a second substrate may be caused to contact the polishing pad 10 at or near a center of the polishing pad 10. In both of these examples, the optical sensor 40 may not be in a suitable position to access the substrate for a reliable endpoint detection metric to be obtained.

What is needed is a CMP polishing station and polishing pad that is configured to adapt to various polishing motions and positional changes of the substrate being polished, which will provide enhanced flexibility and/or provide a more reliable endpoint detection metric.

SUMMARY OF THE INVENTION

Embodiments described herein provide a method and apparatus for detecting and obtaining a metric indicative of a polishing process. The apparatus includes a polishing pad having an optically transparent region adapted to obtain polishing metric from at least one substrate from at least two distinct radial positions of the polishing pad. The method includes obtaining a polishing metric from at least two substrates being polished simultaneously on a single polishing pad.

In one embodiment, a polishing pad assembly is described. The polishing pad includes a circular body comprising a polishing material having a polishing surface, and at least two portions formed in the polishing surface that are transparent to light and electromagnetic radiation, each of the at least two portions comprising a transmissive window disposed below a plane defined by the polishing surface and the transmissive window is coupled to the body by a bonding agent.

In another embodiment, a polishing pad assembly is described. The polishing pad assembly includes a circular body comprising a polishing material having a polishing surface, and a linear strip positioned along a portion of the radius of the polishing surface that is transparent to light and electromagnetic radiation, the linear strip occupying at least one half of the radius of the polishing surface and comprising a transmissive window coupled to the body by a bonding agent and disposed below a plane defined by the polishing surface.

In another embodiment, a method for obtaining a polishing metric while polishing at least two substrates simultaneously on a single circular polishing pad is described. The method includes providing rotational movement of the polishing pad relative to each of the at least two substrates, providing at least one optical sensor in selective communication with a surface of both of the at least two substrates at different radial positions, emitting light or an electromagnetic signal toward each substrate at intervals corresponding with the rotational movement of the polishing pad, and receiving a reflected signal from a surface of at least one of the substrates indicative of polishing progress.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 is cross-sectional view of a conventional chemical mechanical polishing station according to the prior art.

FIG. 2 is a cross-sectional view of one embodiment of a chemical mechanical polishing station.

FIG. 3 is a cross-sectional view of a portion of one embodiment of polishing pad.

FIG. 4 is a top view of one embodiment of a polishing pad.

FIG. 5 is a top view of another embodiment of a polishing pad.

FIG. 6 is a top view of another embodiment of a polishing pad.

FIG. 7 is a top view of another embodiment of a polishing pad.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.

DETAILED DESCRIPTION

Embodiments described herein provide a polishing system and pad assembly suitable for use in a polishing process. The polishing system and pad assembly is capable of providing a metric indicative of polishing performance at any radial location or radial area of the polishing pad surface and/or facilitate endpoint detection of a polishing process at multiple locations of the polishing pad surface. In one embodiment, a polishing system is described that is adapted to perform a polishing process on at least two substrates simultaneously while providing a polishing metric, such as endpoint data, on each of the at least two substrates.

FIG. 2 shows a simplified view of a chemical mechanical polishing (CMP) station 200, partly in cross-section, that may be a stand-alone unit or part of a larger polishing system. The CMP station 200 includes a platen 220 with a polishing pad 210 mounted thereon. In this embodiment, the CMP station 200 includes two carrier head assemblies shown as 230A and 230B. Each carrier head assembly 230A, 230B is adapted to hold substrates, such as semiconductor substrates 215A, 215B, respectively, to be polished. Each carrier head assembly 230A, 230B is configured to urge the respective substrate against the upper surface of the polishing pad 210. The polishing pad 210 has an upper surface serving as a polishing surface 218, which is brought into sliding contact with each substrate 215A, 215B to be polished. A polishing liquid supply nozzle 222 is disposed above the platen 220 for supplying a polishing liquid 219 onto the polishing pad 210.

The polishing pad 210 also includes one or more windows, such as a window W₁ and W₂ that are formed or disposed in the polishing pad 210. Each of the one or more windows W₁ and W₂ are positioned in the polishing pad 210 to provide enhanced access to an optical sensor at more than one location on the polishing pad 210. Additionally, if a single window is used, the single window provides a larger opening in the polishing pad 210 to provide a large access area to the optical sensor for endpoint detection and process monitoring.

The polishing pad 210 may be a polymer material, which may be solely dielectric to facilitate removal of materials from each of the substrates 215A, 215B. Alternatively, the polishing pad 210 may be at least partially conductive to facilitate electrochemical dissolution of material from the each of the substrates 215A, 215B in an electrochemical mechanical polishing (ECMP) process. Suitable polymeric materials that may be used include polyurethane, polycarbonate, fluoropolymers, PTFE, PTFA, polyphenylene sulfide (PPS), or combinations thereof, and other polishing materials used in polishing substrate surfaces. In one embodiment, polishing pad 210 includes at least a polishing surface made of a polymeric material, such as open-pored or closed-pored polyurethane material typically used in the fabrication of polishing pads for service in the polishing of semiconductor wafers. In another application, the polishing pad 210 may contain fixed abrasives. Thus, the polishing liquid 219 may be a slurry or an electrolytic fluid depending on the polishing process used.

While only two carrier head assemblies 230A, 230B are shown, more carrier heads may be provided to hold additional substrates so that the surface area of polishing pad 210 may be used efficiently. Thus, the number of carrier head assemblies adapted to hold substrates for a simultaneous polishing process may be based, at least in part, on the surface area of the polishing pad 210. While only one polishing liquid supply nozzle 222 is shown, additional nozzles, such as one or more dedicated polishing liquid supply nozzles per carrier head assembly may be used.

The platen 220 is coupled to a shaft 242 and a motor 221 to rotate the platen 220 and the polishing pad 210 about an axis. Each of the carrier head assemblies 230A, 230B are coupled to a shaft 232A, 232B, which may be coupled to a motor and a lifting/lowering device (not shown) that is adapted to urge the respective substrates 215A, 215B against the polishing surface 218 of the polishing pad 210. The carrier head assemblies 230A, 230B may be rotatable to provide movement of the respective substrates 215A, 215B relative to the polishing pad 210. The carrier head assemblies 230A, 230B may also be adapted to sweep the respective substrates 215A, 215B in a linear or arcuate motion across the polishing surface 218 of polishing pad 210. In one embodiment, the carrier head assemblies 230A, 230B are disposed on a circular track (not shown) mounted above the polishing pad 210.

At least one optical sensor 240A is provided on the CMP station 200 for measuring a thickness of an insulating film (or layer) or a metallic film (or layer) formed on the surface of the substrates 215A, 215B. As an option, an additional optical sensor 240B may be coupled to the CMP station 200. In one embodiment, the optical sensor 240A is coupled to a base 235 and is stationary relative to any rotational movement of the platen 220 and/or the polishing pad 210.

In one embodiment, the optical sensor 240A is movable, at least in a linear direction, relative to the platen 220 and/or the polishing pad 210. One or both of the platen 220 and the base 235 may include a recessed portion and a track 205A disposed therein allowing linear movement of the optical sensor 240A (and 240B). In one embodiment, the optical sensor 240A may be coupled to the track 205A disposed on the base 235 and movable along the track by a linear actuator 250, such as a servo or stepper motor, or a magnetic actuator. In one application, the optical sensor 240A is configured to be selectively positioned at different positions along at least one half of a dimension of the base 235 or the polishing pad 210, as chosen by the user or determined by the polishing parameters, in order to align with one or more windows formed in the polishing pad 210.

In another embodiment, the optical sensor 240B is coupled in or on the platen 220 and configured to rotate with the platen 220 and polishing pad 210. In this embodiment, the optical sensor 240B may be coupled to a linear track 205B disposed on a lower surface of the platen 220 and is movable along the track by a linear actuator 250, such as a servo or stepper motor, or a magnetic actuator. In one application, the optical sensor 240B is configured to be selectively positioned at differing radial positions along at least one half of a dimension of the platen 220 and/or polishing pad 210, as chosen by the user or determined by the polishing parameters, in order to align with one or more windows, such as window W₁ and window W₂ formed in the polishing pad 210. In this embodiment, electrical connections or wires may be disposed through the shaft 242, or a wireless electrical and signal connection may be provided to control the optical sensor 240B. The optical sensor 240B may be a light-emitting element and a light-detecting element or an electromagnetic signal transmitter/receiver.

FIG. 3 is a cross-sectional view of a portion of one embodiment of polishing pad 210. The polishing pad 210 includes a body 350, which includes a polishing layer 360, a supporting layer 370 and an adhesive layer 380 enabling adhesion to the platen. The polishing pad 210 also includes one or more optical windows 341 (only one is shown in the cross-sectional portion of polishing pad 210 shown in FIG. 3). The polishing layer 360 can include a compressible material, such as a polymeric foam, and has a polishing surface 362. The polishing layer 360 can be grown on the supporting layer 370 or a pressure sensitive adhesive (PSA) layer may be disposed between the polishing layer 360 and the supporting layer 370. For example, a polymer layer can be grown on supporting layer 370 to form the polishing layer 360 so that a PSA layer is not needed between the supporting layer 370 and polishing layer 360.

An opening 322 extends through polishing layer 360 to house a transmissive window 390, which is transparent to light or electromagnetic radiation. The transmissive window 390 can be formed of one or more polymeric materials, such as, a polyurethane or a halogenated polymer (e.g., polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), or polytetra-fluoroethylene (PTFE)). In some embodiments, the transmissive window 390 can be formed of a material having a Shore D hardness of from about 20-80. If the hardness for the material for transmissive window 390 is not within a desired range, two materials having two different hardness can be combined to provide a material with hardness in the desired range. For example, liquid forms of two materials having two different hardness can be combined in a ratio calculated to achieve the desired hardness, then the combined material can be cured and cut to size to form transmissive window 390.

A window recess 396 may be defined between the plane in which polishing surface 362 lies and the plane in which the upper surface of the transmissive window 390 lies. The window recess 396 is designed to be of a predetermined depth D to ensure that when the compressible material forming the polishing layer 360 is compressed, the transmissive window 390 does not extend beyond the polishing layer 360 and contact the substrate that is being polished. The predetermined depth of the window recess 396 is also designed to be small enough so that air bubbles do not form in any chemical polishing solution that leaks between transmissive window 390 and a substrate during polishing. For example, the window recess 396 can be 3-4 mils deep. Selection of a specific depth to ensure that the transmissive window 390 does not contact a substrate may be determined by the compressibility of the polishing layer 360 and the load applied to the substrate during polishing. In some applications, the upper surface of the transmissive window 390 may at least incidentally contact the substrate being polished. In this application, the transmissive window 390 may be adapted to provide a polishing surface.

In some embodiments, an opening is formed through the supporting layer 370 to allow the optical sensor 240A (and/or 240B) (FIG. 2)) to monitor the substrate. However, in the embodiment shown in FIG. 3, the supporting layer 370 does not include an opening below the transmissive window 390. In this embodiment, the supporting layer 370 may be formed from a transparent material to allow monitoring of polishing progress through the material. The supporting layer 370 can be formed of an incompressible and fluid-impermeable polymer. For example, supporting layer 370 can be formed of polyethylene terephthalate (“PET”) or a MYLAR® material.

The transmissive window 390 is secured to supporting layer 370 by a window bonding adhesive 394. The transmissive window 390 can be bonded using window bonding adhesive 394 directly to the supporting layer 370 (as shown in FIG. 3), or to an optional adhesive or PSA layer between supporting layer 370 and polishing layer 360 (not shown). Alternatively, the transmissive window 390 could be adhered directly to the adhesive layer disposed between the supporting layer 370 and the polishing layer 360 (without the window bonding layer). The window bonding adhesive 394 is composed of a material that seals any gap between the transmissive window 390 support layer, such as supporting layer 370 or a PSA layer, and transmissive window 390. The window bonding adhesive 394 also supports the transmissive window 390 against shear stress during polishing. The window bonding adhesive 394 can include an adhesive sealant, such as a viscous rubber-like glue. For example, for some PSA layers, the window bonding adhesive 394 can include one-part room temperature vulcanizing (“RTV”) silicone TSE399™ or TSE397™ materials, which are distributed by GE Silicones of Waterford, N.Y.

FIG. 4 is a top view of one embodiment of a polishing pad 210 having two optical windows 441A and 441B that may be similar to the optical window 341 described in FIG. 3. The first optical window 441A is positioned at a first radial location along a first radial path R₁ of substrate 415A and the second optical window 441B is positioned along a second radial path R₂ of substrate 415B. In one embodiment, R₁ and R₂ are equal such that both optical windows 441A, 441B are positioned the same distance from the center C of the polishing pad 210. In this embodiment, the substrates 415A and 415B are rotated relative to the rotating polishing pad 210 and additionally sweep relative to the rotating polishing pad 210 in a direction generally indicated as sweep paths 405A and 405B, and each optical window is positioned to allow light or an electromagnetic signal from the optical sensor (FIG. 2) to impinge the center of the respective sweep path 405A and 405B. While each of the sweep paths 405A and 405B are shown as linear, it is understood that the sweep path may be arcuate as well.

While not shown, a single, movable optical sensor (240A or 240B of FIG. 2) is aligned with the first optical window 441A and second optical window 441B during each revolution of the polishing pad 210. Alternatively, the optical sensor is aligned with the first optical window 441A and second optical window 441B at a specified interval or intervals based on one or more revolutions of the polishing pad 210. For example, the controller (FIG. 2) contains an algorithm allowing the optical sensor to move between the two optical windows 441A and 441B corresponding with each revolution of the polishing pad 210. Alternatively, the single optical sensor may move between the two optical windows 441A and 441B at alternating intervals based on a fraction of one revolution of the polishing pad 210. In one application, the optical sensor may alternate between optical windows 441A, 441B at every other revolution. In another application, the optical sensor may move between the two optical windows at or about each half revolution of the polishing pad 210. Alternatively, two optical sensors (240A and 240B of FIG. 2) may be dedicated to and positioned to align with each optical window 441A, 441B. In this manner, an endpoint metric may be provided for each substrate 415A and 415B as the respective substrate passes an optical window at each revolution, or at any specified periodicity.

In another application, the optical windows 441A, 441B may be positioned at a specific radius or distance from the center C to overlap with a sweep path of either or both of the substrates 415A, 415B in a manner that provides an endpoint metric at different locations on a single substrate. For example, substrate 415A and its respective sweep path 405A may be centered at R₁, which is the same radial position of optical window 441A. While an algorithm may be provided to provide a signal and metric as the substantial geometric center of substrate 415A passes optical window 441A, the optical window 441B may provide a signal and a metric from another portion of substrate 415A. Alternatively, an algorithm may be provided to provide a signal and metric as any portion of the substrate 415A passes optical window 441A and the optical window 441B may provide a signal and a metric from a different portion of substrate 415A. This allows more accurate endpoint determination as the periodicity is increased and/or a greater surface of the substrate is surveyed. In one example, an endpoint metric may be obtained from a center of the substrate and another endpoint metric may be obtained from a periphery of the same substrate at each revolution of the polishing pad 210 (or at any specified periodicity), which in this example is substrate 415A.

FIG. 5 is a top view of another embodiment of a polishing pad 210 having four optical windows 541A-541D, wherein each optical window 541A-541D may be similar to the optical window 341 described in FIG. 3. In this embodiment, each optical window 541A-541D is positioned at four specific radial locations on the polishing pad 210. While the pattern of optical windows 541A-541D are shown in an arcuate or spiral pattern on the polishing pad 210, the optical windows 541A-541D may be any pattern, such as in a cross-shape or X shape, or a linear pattern. Additionally, while four optical windows 541A-541D are shown, the polishing pad 210 may have any number of windows.

FIG. 6 is a top view of another embodiment of a polishing pad 210. In this embodiment, the polishing pad includes five optical windows 641A-641E that may be similar to the optical window 341 shown in FIG. 3. The optical windows 641A-641E are arranged in a linear fashion, such as in a radial line. In this embodiment, the optical windows 641A-641E are separated by polishing material 662, which is part of the polishing surface of the polishing pad 210. Although five optical windows 641A-641E are shown, any number of optical windows may be used.

Collectively, the optical windows 641A-641E and polishing material 662 between each optical window covers at least about one half of the radius of the polishing pad 210. For example, if the polishing pad 210 has a diameter of about 42 inches, which corresponds to a radius of 21 inches, the collective length of the optical windows 641A-641E and polishing material 662 between each optical window covers at least about 10.5 inches. In another embodiment, the optical windows 641A-641E and polishing material 662 between each optical window collectively covers at least about 75% to about 90% of the radius of the polishing pad 210. For example, if the polishing pad 210 has a diameter of about 42 inches, which corresponds to a radius of 21 inches, the collective length of the optical windows 641A-641E and polishing material 662 between each optical window covers about 15.7 inches to about 18.9 inches.

In another embodiment, the optical windows 641A-641E may be spaced along the radial line in a manner that spaces each optical window at specific radial distances from center C and/or an outside diameter of the polishing pad 210. In one example, if the polishing pad 210 has a diameter of about 42 inches, which corresponds to a radius of 21 inches, the center of each optical window 641A-641E may be spaced at about 4 inch increments. In another embodiment, the perimeter optical window 641E may be spaced about 1-2 inches from the outer diameter of the polishing pad 210, and the remaining optical windows may be spaced, either equally or unequally, towards the center C.

FIG. 7 is a top view of another embodiment of a polishing pad 210. In this embodiment, the polishing pad includes a single radially elongated optical window 741 that may be similar to the optical window 341 shown in FIG. 3, with the exception of occupying a greater portion of the area of the polishing pad 210. In this embodiment, the optical window 741 is arranged in a linear fashion, such as in a line corresponding to a radius, and includes no polishing material therebetween. While the optical window 741 is disposed along a radius of the polishing pad 210, the optical window 741 may be disposed on the polishing pad 210 as a chord, or a segment thereof (not shown). In another embodiment (not shown), optical window 741 may be formed as an arc.

In the embodiments shown in FIGS. 5-7, a single, movable optical sensor, such as optical sensor 240A or 240B (FIG. 2) is aligned with the optical windows 541A-541D or 641A-641E, or at various points along the single optical window 741 during each revolution of the polishing pad 210, or at specified intervals, such as every half revolution or every other revolution of the polishing pad 210. For example, the controller (FIG. 2) contains an algorithm allowing the optical sensor to move between various positions corresponding with each revolution of the polishing pad 210, or the optical sensor may move between positions to align with the optical window(s) at alternating revolutionary intervals, such as half revolutions, one-quarter revolutions, among other intervals. Alternatively, more than one optical sensor may be dedicated to and positioned to align with one or more of the optical windows 541A-541D or 641A-641E. In another alternative, more than one optical sensor may be positioned, either fixed or movable relative to the polishing pad 210 and/or platen (not shown), to be aligned with various points along the single optical window 741 at each revolution or at any specified periodicity. In this manner, an endpoint metric may be provided for one or more substrates as the respective substrate passes an optical window and/or optical sensor at each revolution, or at any specified periodicity. In yet another application, at least one optical sensor may be configured to align with one or more optical sensors to provide an endpoint metric at more than one location on a single substrate.

The inventive polishing pad is configured to adapt to various polishing motions and/or positional changes of a substrate or substrates being polished on the pad. The polishing pad as described herein provides enhanced flexibility and/or a more reliable endpoint detection metric of the substrate or substrates being polished. Modification of a polishing pad as described herein minimizes the available polishing surface of the polishing pad as additional sections of the polishing surface are removed for installation of additional or larger windows. Further, properties of the pad, such as flatness, hardness and other properties are changed when additional or larger windows are added. Thus, modification of a polishing pad meets general reluctance in the field due to the aforementioned problems. However, the inventive polishing pad with multiple and/or larger windows has provided a more precise endpoint metric and enables an endpoint metric at a greater frequency.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

1. A polishing pad assembly, comprising: a circular body comprising a polishing material having a polishing surface; and at least two portions formed in the polishing surface that are transparent to light and electromagnetic radiation, each of the at least two portions comprising a transmissive window disposed below a plane defined by the polishing surface and the transmissive window is coupled to the body by a bonding agent.
 2. The polishing pad assembly of claim 1, wherein the at least two portions are disposed at different radial positions within the circular body.
 3. The polishing pad assembly of claim 1, wherein the circular body comprises a supporting layer.
 4. The polishing pad assembly of claim 3, wherein the transmissive window is adhered to the supporting layer.
 5. The polishing pad assembly of claim 3, wherein the supporting layer comprises a material that is transparent to light and electromagnetic radiation.
 6. The polishing pad assembly of claim 3, wherein the at least two portions are disposed in the supporting layer.
 7. The polishing pad assembly of claim 1, wherein the circular body comprises an adhesive layer opposite the polishing surface.
 8. The polishing pad assembly of claim 7, wherein the adhesive layer is transparent to light and electromagnetic radiation.
 9. A polishing pad assembly, comprising: a circular body comprising a polishing material having a polishing surface; and a linear strip positioned along a portion of the radius of the polishing surface that is transparent to light and electromagnetic radiation, the linear strip occupying at least one half of the radius of the polishing surface and comprising a transmissive window coupled to the body by a bonding agent and disposed below a plane defined by the polishing surface.
 10. The polishing pad assembly of claim 9, wherein the circular body comprises a supporting layer.
 11. The polishing pad assembly of claim 10, wherein the transmissive window is adhered to the supporting layer.
 12. The polishing pad assembly of claim 10, wherein the supporting layer comprises a material that is transparent to light and electromagnetic radiation.
 13. The polishing pad assembly of claim 9, wherein the linear strip comprises one or more optical windows separated by a polishing material.
 14. The polishing pad assembly of claim 9, wherein the linear strip occupies about 75% of the radius of the polishing surface.
 15. The polishing pad assembly of claim 9, wherein the linear strip occupies about 90% of the radius of the polishing surface.
 16. A method for obtaining a polishing metric while polishing at least two substrates simultaneously on a single circular polishing pad, comprising: providing rotational movement of the polishing pad relative to each of the at least two substrates; providing at least one optical sensor in selective communication with a surface of both of the at least two substrates at different radial positions; emitting light or an electromagnetic signal toward each substrate at an interval corresponding with the rotational movement of the polishing pad; and receiving a reflected signal from a surface of at least one of the substrates indicative of polishing progress.
 17. The method of claim 16, further comprising: moving the at least one optical sensor to different radial positions at each revolution of the polishing pad.
 18. The method of claim 16, further comprising: moving the at least one optical sensor to different radial positions at substantially each half revolution of the polishing pad.
 19. The method of claim 16, wherein the interval equals one revolution of the polishing pad.
 20. The method of claim 16, wherein the interval equals every other revolution of the polishing pad. 